1. Field of the Invention
The invention relates to a memory element and fabrication method thereof, and more particularly to a phase-change memory element and fabrication method thereof.
2. Description of the Related Art
Electronic devices use different types of memories, such as DRAM, SRAM and flash memory or a combination based on the requirements of the application, the operating speed, the memory size and the cost considerations of the equipment. Current developments in the memory technology field include FeRAM, MRAM and phase-change memory. Among these alternative memories, phase-change memory is most likely to be mass manufactured in the near future.
Phase-change memory is targeted for applications currently utilizing flash non-volatile memory. Such applications are typically mobile devices which require low power consumption, and hence, minimal programming currents. A phase-change memory cell is designed with several goals in mind: low programming current, higher reliability (including electromigration risk), smaller cell size, and faster phase transformation speed. These requirements often set contradictory requirements on feature size, but a careful choice and arrangement of materials used for the components can often widen the tolerance.
To reduce the programming current, the most straightforward way is to shrink the heating area. A benefit of this strategy is simultaneous reduction of cell size. Assuming a fixed required current density, the current will shrink in proportion to the area. In reality, however, cooling becomes significant for smaller structures, and loss to surroundings becomes more important due to increasing surface/volume ratio. As a result, the required current density must increase as heating area is reduced. This poses an electromigration concern for reliability. Hence, it is important to use materials in the cell which do not pose an electromigration concern. It is also important to improve the heating efficiency, by increasing heating flux in the active programming region while reducing heat loss to the surroundings.
U.S. Pat. No. 6,750,079 discloses a method for fabricating a phase-change memory element 10, referring to FIG. 1. First, a dielectric layer 14 with a perpendicular side wall formed on a substrate 12. Next, a metal layer is conformally formed on the dielectric layer 14 and substrate 12. Next, the metal layer is subjected to an anisotropic etching to form a metal spacer 16 with smaller top surface. Next, a dielectric layer 18 is formed to cover the side walls of the metal spacer 16. Finally, a phase-change layer 20, an electrode 22 and a protective layer 24 are subsequently formed on the substrate.
Therefore, it is necessary to develop a phase-change memory to solve the previously described problems.